Dean Corso is a cynical, ruthless rare-book dealer in New York who cares far more about profit than the intrinsic value of literature. Hired by wealthy, eccentric bibliophile Boris Balkan, Corso is tasked with authenticating a notoriously rare and demonic seventeenth-century volume titled *The Nine Gates of the Kingdom of Shadows*. Written by elusive author Aristide Torchia, supposedly in collaboration with the Devil himself, only three copies are known to exist worldwide. Balkan possesses one and suspects the other two are forgeries. He charges Corso with traveling to Europe to inspect the remaining copies held by rival collectors, aiming to assemble the true gateway to ultimate infernal power.Corso’s investigation immediately turns perilous. In Toledo, Spain, he visits the wealthy Varda brothers, only to find the older brother murdered in a manner mimicking an illustration from Torchia’s book. Before leaving, Corso discovers subtle discrepancies in the woodcuts, confirming each copy contains different illustrations, and together they form a nine-step puzzle. As Corso travels across Europe to Portugal and Paris to examine the final two volumes, he is stalked by a mysterious, supernatural young woman who possesses preternatural agility and strength. She repeatedly saves Corso from assassins working for Liana Penta, the unstable widow of the Spanish collector, who desperately wants the book back to complete the ritual herself.Throughout the harrowing ordeal, the mysterious
guardian angel acts as Corso's protector, guiding him through a labyrinth of murder, theft, and arcane secrets. Corso slowly realizes that the nine distinct engravings hidden across the three volumes are not merely artistic oddities. When arranged in a precise sequence using a secret ninth illustration, they serve as a mystical map designed to summon the Devil and grant immortality to whoever successfully completes the incantations.Balkan ultimately steals the assembled book, kidnapping Corso and Liana to witness his crowning achievement. In an abandoned castle, Balkan performs the black mass, reciting the verses while standing inside a flaming pentagram. However, because one of the crucial engravings used by Balkan was a clever forgery planted earlier, the ritual backfires. Instead of receiving infernal dominion, Balkan is engulfed in roaring flames, screaming as he burns to death.Escaping the burning ruins, Corso reunites with his supernatural protector, who reveals her true identity as the
fallen angel or succubus depicted in Torchia’s woodcuts. They share a passionate encounter before she vanishes into the dawn. Empowered by the ordeal and now holding the key to the ultimate secret, Corso secures the final missing, authentic engraving and triumphantly approaches the gleaming, mythical Ninth Gate, forever transformed by his journey into darkness.